Light-emitting-diode (LED) with spherical lens

ABSTRACT

A light-emitting diode has a lens secured in self-adjusted fashion to a mesa surface of a semiconductor body by means of adhesive. The mesa surface is substantially perpendicular and centered with an emission axis of the light-emitting diode. Preferably, the lens is spherical and the mesa surface has a diameter comparable to or smaller than a diameter of the lens.

This is a division of application Ser. No. 906,900, filed Sept. 15, 1986now U.S. Pat. No. 4,740,259.

BACKGROUND OF THE INVENTION

The present invention relates to a light-emitting diode wherein aspherical lens is secured by adhesive to a semiconductor body having aluminescent zone therein with the shape of a spot. The luminescent zoneis situated closer to one surface of the semiconductor body than anopposite surface thereof.

In optical communications technology, it is known to employlight-emitting semiconductor diodes, referred to as luminescent diodes(LED), in combination with glass fibers. Such a luminescent diodegenerally emits the radiation generated in it in all directions, or atleast with an extremely large aperture angle. In order to be able tocouple optimally high light power of the luminescent diode into aprovided glass fiber, it is standard to provide the luminescent diodewith a spherical lens for concentrating the radiation.

Such a luminescent diode has a semiconductor body. Under givenconditions, this is formed of a substrate body and of one or moreepitaxial layers applied to one of its surfaces. The actuallight-emitting zone has the shape of a spot. The provided sphericallens, particularly a spherical lens, is applied to the semiconductorbody or substrate body and is adjusted such that the focal point of thelens and this spot-shaped zone of the luminescent diode lie close to oneanother in known manner. A preferred technique for securing thisspherical lens to the semiconductor body is the gluing of the lens. Itis extremely involved, but necessary, to guarantee that the lens issituated in a central position relative to the zone forming theluminescent spot.

The employment of spheres as a lens for such luminescent diodes is knownprior art. For example, see U.S. Pat. No. 4,501,637 incorporated hereinand German A No. 32 32 526.

The figures of U.S. Pat. No. 4,501,637 show the sequence of themanufacturing method of a luminescent diode having a spherical lenssituated thereon. Close to the one substrate surface the luminescentzone therein is prepared in the semiconductor substrate. A layer is thenapplied to the surface adjacent to this luminescent zone, a ring beingproduced by etching from this layer in adjustment relative to theluminescent zone. This ring serves for the acceptance or adjustment ofthe spherical lens. When applied and seated on this ring, it is thenheld at this ring and the substrate member with adhesive.

German A No. 32 32 526 discloses an integrated luminescent diodecomprising a plurality of light-emitting regions in a shared substratemember. Each and every light-emitting region has a spherical lensallocated to it. The spacings of the light-emitting regions from oneanother are adapted to the diameter of the spherical lenses such thatthe distribution of the light-emitting regions in the substrate memberand the spherical lenses applied to the substrate surface in thedensest, planar sphere packing are arranged in adjusted fashion relativeto one another. The individual spherical lenses thus abut tightlyagainst one another. Adhesive with which the spherical lenses are heldat the substrate member and relative to one another is situated in theclearances between these spheres. It is also provided in the arrangementof this publication that a depression adjusted relative to theindividual light-emitting region is present on the substrate surface orin layers applied to the substrate surface, this depression potentiallyserving the purpose of adjusting the spherical lenses.

In the arrangement of this publication, the light-emitting regions lieclose to that surface which carries the layers comprising the adjustingdepressions. These depressions were to be previously employed in themethod of manufacturing the light-emitting regions.

A frequently employed method for manufacturing a luminescent diode onwhich only a single spherical lens is situated (such as the luminescentdiode of U.S. Pat. No. 4,501,637 but not that of German A No. 32 32 526)is the application of the spherical lens with manipulation thereof. Forexample, the correct position of the spherical lens is monitored byobservation with the assistance of a magnifying glass. It must,therefore, also be incured that a lateral dislocation of the lens on thesurface of the substrate member does not occur.

SUMMARY OF THE INVENTION

An object of the present invention is to specify a simplified way bywhich an adjusted fastening of the spherical lens to the semiconductorbody of the luminescent diode can be implemented.

This object is achieved with a luminescent diode apparatus wherein asemiconductor body has near one surface a luminescent zone. At anopposite surface further away from the luminescent zone a circular mesawith a mesa surface is provided. The mesa surface is positioned inadjusted and centered fashion opposite the luminescent zone of thediode. A diameter of the mesa surface is dimensioned of approximatelycomparable size compared to a diameter of the lens. The spherical lensis arranged on the mesa surface.

The invention is based on the idea of achieving the occurrence of aself-adjusting effect in the course of the application of the sphericallens to the surface of the semiconductor body of the luminescent diode.This is achieved in accordance with the invention in that the onesurface at the semiconductor body is fashioned with a circular mesa.This mesa has a mesa diameter, i.e. a diameter of the actual mesasurface, which is dimensioned such that it exhibits comparable sizecompared to the diameter of the lens. It is preferably smaller, or atleast not significantly larger, than this lens diameter. This dimensionguarantees that the spherical lens applied given a still viscousadhesive on the mesa surface is held in self-adjusted fashion in thecenter of the mesa due to the surface tensions of the viscous adhesiveuntil the final hardening of the adhesive. Too large a diameter of themesa surface would lead to a less precise self-adjustment. Also, toosmall a diameter unnecessarily restricts the through opening of thesemiconductor body for the transfer of the radiation from theluminescent spot into the lens. The inventive matching of the diameterof the mesa and of the lens relative to one another is important for theinvention but, given knowledge of the present invention, this matchingcan then be specified for the person skilled in the art on acase-by-case basis. The mesa has a height which is at least sufficientlyhigh such that the adhesive employed at least does not substantiallymoisten those surface parts of the semiconductor body which already lieto the side of the actual mesa. For the sake of simplicity, the mesa isfashioned on the one surface of the semiconductor body which liesopposite that surface of this semiconductor body in whose proximity theaforementioned zone of the luminescent spot is situated. What isrequired for this purpose is that the semiconductor body is at leastlargely transmissive for the radiation generated in the zone andemitted. This is standard practice in the structure of such a diode,particularly for infrared luminescent diodes.

With reference to the zone of the luminescent spot, the mesa generatedon the semiconductor body is placed in exactly adjusted fashion.Manufacturing such a mesa presents no problem in terms of semiconductortechnology. In particular, the manufacture of the mesa is carried out byetching after previous photolithographic positioning. The light emissionof the luminescent spot can thus be employed, whereby thephotolithographic process can be especially simplified.

U.S. Pat. No. 3,067,485 may also be referenced with respect to themanufacture of a mesa on the semiconductor body of a semiconductordevice. This discloses the manufacture of a mesa wherein the pn-junctionzone is adjacent to the surface of this mesa. This known manufacturingmethod, however, can also be employed in the invention wherein thepn-junction of the zone of the luminescent spot is close to that surfaceof the semiconductor body which lies opposite the other surface of thesemiconductor body containing the mesa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show a known luminescent diode arrangement;

FIG. 3 shows a luminescent diode of the invention;

FIG. 4 shows a semiconductor body before fabrication of the luminescentdiode of FIG. 3;

FIG. 5 shows a preferred manufacturing method; and

FIG. 6 shows a device relating to the manufacturing method of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a plan view and side view, FIGS. 1 and 2 show a known luminescentdiode with a spherical lens. The semiconductor body is referenced 1, andis formed of a substrate body 2 and an epitaxial layer 3 epitaxiallyapplied thereto. The zone of the luminescent spot is referenced 4.

A spherical lens 6 is situated at that surface 5 of the semiconductorbody 1 or substrate body 2 lying opposite the epitaxial layer 3. Thisspherical lens 6 serves the known purpose of concentrating radiation.This lens 6 is secured to the surface 5 by means of the glue 7. As isknown, the dimensions are selected such that, with a given or selectedrefractive index of the material of the spherical lens 6, the distanceof the luminescent spot 4 from the surface 5 and the diameter of thelens are matched to one another such that the focal spot has the desiredor known prescribed position relative to the luminescent spot 4.

It may be seen from FIGS. 1 and 2 that the spherical lens 6 therein isnot precisely adjusted relative to the luminescent spot 4. This can bebased on an inadequately precise application of the spherical lens 6 tothe surface 5 and/or on subsequent distortion of the hardening glue 7.The consequence of such a misadjustment is that the direction of maximumradiation (referenced 8) of this luminescent diode comprising aspherical lens is oblique relative to the diode (for example, relativeto the surface 5). This complicates later incorporation and adjustmentof the known luminescent diode in communication-oriented equipmentprovided for this luminescent diode.

FIG. 3 shows a luminescent diode 10 of the invention comprising aspherical lens 6. Given the diode 10, the semiconductor body isreferenced 11. In particular, this can again be a substrate body 12 withan epitaxial layer 13 situated thereon. The luminescent spot is againreferenced 4.

As may be seen, the semiconductor body 11 or substrate body 12 differsfrom the semiconductor body 1 in that the surface 15 thereof comprises amesa 25. This mesa 25 is circular or has a circular surface 26. Theadhesive is again referenced 7. The spherical lens 6, however, issecured to the mesa surface 26 with this adhesive according to theinvention. Reference numeral 80 indicates the exactly aligned axis ofthe emission.

As may be seen from FIG. 3, the diameter d₂₆ of the mesa surface 26 isof comparable size relative to the diameter d₆ of the spherical lens 6and is preferably somewhat smaller than the latter. It is recommended toselect d₂₆ between 1.2·d₆ and 0.5 d₆, and preferably between 0.7 and 0.9d₆. This dimensioning relationship guarantees an exactly adjustedposition of the spherical lens 6 relative to the luminescent spot 4 ofthe diode 10 and an optimumly large aperture or passageway for theradiation of the luminescent spot 4 into the lens 6.

The manufacture of mesa structures of a semiconductor body or substratebody is known per se. This occurs in a photolithographic way by means ofetching. The technology of photolithography and of etching is highlydeveloped for semiconductor technology, and is also inherently at thecommand of a person skilled in the art. The mesa surface 26 or the mesa25 is precisely adjusted relative to the luminescent spot 4 without thisraising problems for the manufacturing method of the mesa. Inparticular, the radiant emission of the luminescent spot 4 can beemployed for a self-adjusting masking in the photolithographic method ofthe masking to be provided.

The mesa 25 forms a pedestal having a circular surface on which acentered position of the applied spherical lens is guaranteed as aresult of the surface tension of the still viscous adhesive. However,care must be exercised to see that the quantity of adhesive is limitedwith good dosing so that the adhesive essentially moistens only the mesasurface 26. Either the spherical lens 6 or the mesa surface 26 ismoistened with the adhesive before the spherical lens is glued on. Thespherical lens 6 put in place on the mesa surface 26 then remains in itscentered position on this mesa surface 26 even during hardening, and nosignificant quantity of adhesive proceeds onto the side wall surface ofthe mesa.

The necessary teachings for the implementation of the manufacturealready proceed from the above comments. In particular, however, a diode10 in accordance with the principle of the invention is suitable forproduction in great numbers in an integrated manufacturing method. Withsuch an integrated method, the corresponding spherical lenses can besimultaneously applied to a plurality of prepared luminescent diodes inone pass. The diodes are thus still parts of a wafer which is not to bedivided into the individual diodes until later.

FIG. 5 shows a perspective view of a portion of a wafer 51 formed of asemiconductor material such as also employed for the bodies 1 and 11. Onthe surface 55 of the wafer 51, one can see a number of mesas 25 whichare preferably regularly distributed. These mesas 25 are manufactured bya photolithographic and etching-oriented method already discussed above.FIG. 5 shows the wafer 51 in that condition in which the respective mesasurface 26 is already provided with adhesive 7. This has advantageouslyoccurred in that these mesa surfaces 26 have been brought into contactwith an adhesive film 56 which is situated on a carrier plate 57 shownarranged above the wafer 51 in FIG. 5. As a result of this contact ofthe mesa surfaces 26 of the wafer 51 with the adhesive film 56, acorresponding transfer of the adhesive 7 occurs.

FIG. 6 shows a technique of the method for the application of thespherical lenses 6 to the mesa surfaces 26 of the wafer 51. There, anunderpressure or vacuum apparatus 61 is provided, the spherical lenses 6being held by suction in the openings 62 thereof. The two-dimensionalgrid of this means 61 is identical to the grid of the mesas 25 of thewafer 51. By bringing the means 61 and the wafer 51 into contact withone another, the emplacement of the spherical lenses 6 onto the mesasurfaces 26 occurs, i.e. the impression of the spherical lenses 6 intothe respective adhesive 7 results. Let it be pointed out that theadhesive in FIG. 5 can also be applied in identical amounts to thespherical lenses 6 in the means 61 in an analogously correspondingfashion.

After interruption of the underpressure in the means 61 and removal ofthe means 61, the spherical lenses 6 remain on the respective mesasurfaces 26. As a consequence of the inventively provided mesas 25,there is no need of a special, additional adjustment of the sphericallens to the respective luminescent diode 10a, 10b, 10c, etc. in theinvention given this integrated method. These individual luminescentdiodes 10a . . . are obtained in that, in accordance with a knownmethod, the wafer 51 is divided at the dotted lines, particularly byscoring.

Let a dimensioning example also be recited below. A rectangularsemiconductor body 11 has, for example, the edge dimensions 25 μm and150 μm. Providing the somewhat long form is recommended for the purposeof an easier bonding of the leads. For such a diode, the spherical lens6 has a diameter of about 100 μm. The mesa diameter d₂₆ of the mesasurface 26 is dimensioned from about 50 through 120 μm, particularly 70to 90 μm. This corresponds to the criterion specified above andguarantees the self-adjustment of the invention. Also, more generallythese figures correspond to the diameter of the mesa surface beingdimensioned between 0.5 and 1.2 times the diameter of the lens and moreparticularly between 0.7 to 0.9 times the diameter of the lens. Theheight of the mesa 25 amounts, for example, to 20 μm given, for example,a 60 μm thickness of the semiconductor body 11 outside of the region ofthe mesa 25. The luminescent zone or the luminescent spot 4 is situatedat a distance of a few μm from the surface 13.

Although various minor changes and modifications might be proposed bythose skilled in the art, it will be understood that I wish to includewithin the claims of the patent warranted hereon all such changes andmodifications as reasonably come within my contribution to the art.

I claim as my invention:
 1. A light-emitting diode apparatus,comprising:spherical lens means for radiation concentration secured to alight-emitting diode by means of adhesive; said light-emitting diodehaving a semiconductor body with a luminescent zone which has a shape ofa spot; the luminescent zone being situated closer to one surface ofsaid semiconductor body than an opposite surface thereof; the oppositesurface having a mesa with a circular mesa surface, the circular mesasurface being positioned in adjusted and centered fashion opposite theluminescent zone of the diode; the spherical lens means being arrangedon the circular mesa surface, and being aligned and retained inself-centered fashion on the mesa surface by the adhesive; a diameter ofthe circular mesa surface being dimensioned of a comparable size to adiameter of such that the spherical lens is self-centered by a surfacetension of the adhesive when viscous in combination with the mesasurface diameter.
 2. A light-emitting diode apparatus according to claim1 wherein the diameter of the circular mesa surface is dimensionedbetween 1.2 to 0.5 times a diameter of the lens means.
 3. Alight-emitting diode apparatus according to claim I wherein the diameterof the circular mesa surface is dimensioned between 0.7 to 0.9 times thediameter of the lens means.
 4. A light-emitting diode apparatusaccording to claim 1 wherein to mesa is an etched mesa.
 5. Alight-emitting diode apparatus, comprising:a substrate body having alayer at one surface thereof and a luminescent spot zone in a region ofa junction between the layer and the substrate body; at a surface of thesubstrate body opposite the layer a spherical lens being arranged, saidopposite surface being substantially perpendicular to an axis ofemission from the luminescent zone through the substrate body; a mesastructure having a circular mesa surface which is perpendicular to saidaxis of emission; the spherical lens being positioned and centered onthe mesa surface and symmetrical to said axis of emission from theluminescent spot zone, and being retained thereby adhesive; and meansfor self-centering the spherical lens on the mesa surface, said forself-centering comprising a diameter of the circular mesa surface beingdimensioned such that through interaction with the adhesive when it isin a viscous condition, the spherical lens is self-centered on the mesasurfaces by surface tension of the adhesive.
 6. An apparatus accordingto claim 5 wherein a diameter of the circular mesa surface is less thana diameter of the spherical lens.